A transmission is a device in which ratio between a rotational speed of an input shaft and a rotational speed of an output shaft is changeable into several ratios. For example, the transmission is used for, for example, transmitting rotational torque of an engine of a vehicle to a driving wheel at a gear ratio selected depending on running condition of the vehicle. There are several methods for changing gear ratio. For example, there is a transmission that accordingly selects an appropriate gear ratio from gear combinations. The gear combinations, each of which has a different gear ratio, are established within the transmission.
A synchromesh-type transmission having a synchronizer device for achieving smooth shift of the gear combinations is known. The synchronizer device includes a torque transmitting shaft, a clutch hub, a pair of gears and a pair of synchronizer rings. The clutch hub is spline-engaged with the torque transmitting shaft. Each of the pair of the gears is loosely fitted on the torque transmitting shaft and is arranged at each side of the clutch hub. Each of the pair of the synchronizer rings is slidably provided at each of the pair of the gears.
Specifically, the Borg-Warner type synchronizer device, which does not engage the clutch hub and the gear until a synchronizing operation is completed, is well known. Further, a lever-type synchronizer device disclosed in, for example, JP1997089002 and in JP 2004044648A is also adopted to a transmission. The lever-type synchronizer device has a simpler configuration comparing to the Borg-Warner type synchromesh, furthermore, the lever-type synchromesh achieves the same synchronizing operation as the Borg-Warner type synchromesh conducts with less operating force by utilizing a so-called principle of leverage.
Taking a synchromesh provided at an automobile as an example, the synchronizing operation of the lever-type synchromesh will be briefly described in accordance with FIGS. 4, 5 and 6 of the attached drawings. Not all components, but only major components of the synchromesh are illustrated in FIGS. 4, 5 and 6. Several lever-type synchronizer devices are provided at necessary portions of the transmission for synchronizing rotations.
The known lever-type synchronizer device includes a shaft 2 to which the rotational torque of the engine is transmitted, a clutch hub 3 (a first rotating member) fixed at the shaft 2, a gear 4 (a second rotating member) rotatably provided at the shaft 2, a synchronizer ring 5, a C-shaped spring 91, a retracting spring 92, a lever 7 and a sleeve 6 provided at the outermost circumference of the lever-type synchronizer device so as to be slidable along outer circumferences of the clutch hub 3 and the gear 4 in an axial direction of the shaft 2. Starting from the left in FIG. 4A, the synchronizer ring 5, the C-shaped spring 91 and the retracting spring 92 are arranged in this order between the clutch hub 3 and the gear 4. The lever-type synchronizer ring changes a state between the clutch hub 3 and the gear 4 either to a connected state or to a neutral state. The connected state is a state where the lever-type synchronizer device synchronizes clutch hub 3 and the gear 4 that are relatively rotatable in order to integrally rotate the clutch hub 3 and the gear 4. The neutral state is a state where the lever-type synchronizer device disengages connection between the clutch hub 3 and the gear 4 so that the clutch hub 3 and the gear 4 are rotated relative to each other.
A spline 31 is formed on the outer circumference of the clutch hub 3.
A gear body (not shown) and a gear piece 41 (conical body) are integrally formed on the gear 4. The gear body is rotatably supported at the shaft 2 by means of a bearing (not shown). An outer conical surface 411 is formed on one end portion of the gear piece 41 facing the clutch hub 3. A teeth portion 412 is formed on an outer circumference of the other end portion of the gear piece 41. An external diameter of the teeth portion 412 is formed to be equal to an external diameter of the spline 31.
The synchronizer ring 5 includes an inner conical surface 51 contacting the outer conical surface 411 of the gear piece 41 of the gear 4. The synchronizer ring 5 is arranged between the clutch hub 3 and the gear 4 so as to be movable in an axial direction of the shaft 2 relative to the clutch hub 3, and so that the rotation of the synchronizer ring 5, is synchronized with the rotation of the clutch hub 3.
A spline 61 is formed on an inner circumferential surface of the sleeve 6. The spline 61 is engaged with the spline 31 formed on the outer circumference of the clutch hub 3 so that the sleeve 6 is integrally rotated with the clutch hub 3. The sleeve 6 is slidable along the spline 31 of the clutch hub 3 in accordance with an operation of a shift lever (not shown). The sleeve 6 is slidably moved in the axial direction of the shaft 2 to the left in FIG. 4A, and then the sleeve 6 eventually reaches the teeth portion 412 formed on the outer circumference of the gear piece 41 so that the sleeve 6 indirectly connects the spline 31 and the teeth portion 412 in order to synchronize a rotation of the clutch hub 3 with a rotation of the gear 4. As a result, the clutch hub 3 and the gear piece 41 are integrally rotated. Additionally, a recessed portion 63 is formed on the approximately middle of the spline 61 of the sleeve 6 in the axial direction of the shaft 2. Specifically, in this embodiment, as illustrated in FIG. 4A, two recessed portions 63 are formed on the spline 61 so as to face each other.
The lever 7 is arranged between the clutch hub 3 and the synchronizer ring 5. The lever 7 is rotated in the same manner as the clutch hub 3 being rotated, and the lever 7 presses the synchronizer ring 5 towards the gear 4 by the principle of leverage. As illustrated in FIGS. 4A and 5, the lever 7 is formed with an upper half ring-shaped portion and a lower half ring-shaped portion. A key portion 711 is formed on a top portion 71 of each of the upper and the lower half ring-shaped portions along an outer circumference thereof. Further, a protruding portion 721 is formed on one end portion and the other end portion of the upper half ring-shaped portion so as to protrude towards the shaft 2. Similarly, the protruding portion 721 is formed on one end portion and the other end portion of the lower half ring-shaped portion so as to protrude towards the shaft 2.
When the synchromesh is in a neutral state, the key portions 711 are engaged with the recessed portions 63 of the sleeve 6 respectively. As illustrated in FIG. 4B, an inclined surface 64 is formed on one end wall (on the left of the recessed portion 63 in FIG. 4B) and another end wall (on the right of the recessed portion 63 in FIG. 4B) of each of the recessed portions 63 in the axial direction of the shaft 2.
The C-shaped spring 91 is made of a ring-shaped member, and an opening is formed on the C-shaped spring 91. Further, the C-shaped spring 91 is fitted along the inner circumferential surface of the lever 7. The C-shaped spring biases the lever 7 outwardly towards the sleeve 6 (in a radial direction of the lever 7) by elasticity of the C-shaped spring 91.
The retracting spring 92 includes a flat portion 921 formed in a flat ring-shape arranged between the synchronizer ring 5 and the lever 7, and further, the retracting spring 92 includes four leg portions 922 that are diverged from the flat portion 921. As illustrated in FIG. 4A, two of the four leg portions 922 are diverged from a right top portion of the flat portion 921 in FIG. 4A and another two of the four leg portions 922 are diverged from a left top portion of the flat portion 921 in FIG. 4A. A pressing portion 923 is formed on end portion of each of the leg portions 922 that presses the lever 7 towards the clutch hub 3 by elasticity of each of the pressing portion 923. Furthermore, the retracting spring 92 includes fixing portions 924 on an upper top portion and a bottom top portion of the retracting spring 92 for fixing the retracting spring 92 to the clutch hub 3, as illustrated in FIG. 4B. Further, the fixing portions 924 restrain rotation of the retracting spring 92 by fixing the retracting spring 92 to the clutch hub 3. The fixing portions 924 are formed so as to extend through an inner circumference of the lever 7 towards the clutch hub 3.
Synchronizing operation of the lever-type synchronizer device of the known art will be described below in accordance with FIG. 6. Specifically, the synchronizing operation will be described with the upper half ring-shaped portion of the lever 7 as an example. Hereinbelow, the upper half ring-shaped portion is referred to simply as the lever 7 for convenience. The lever-type synchronizer device of the known art is operated in accordance with sliding movement of the sleeve 6. The sleeve 6, the lever 7, the retracting spring 92, the synchronizer ring 5 and the gear piece 41 are schematically illustrated in FIG. 6.
In the neutral state before the sleeve 6 is slid, as illustrated in FIG. 6A, the key portion 711 of the lever 7 is engaged with the recessed portion 63 of the spline 61 formed on the sleeve 6. In this state, the clutch hub 3 (not shown in FIG. 6A) and the gear piece 41 are not integrally rotated.
When the lever-type synchronizer device is in the neutral state, the lever 7 is retained between the clutch hub 3 and the synchronizer ring 5, and the lever 7 receives biasing force from the C-shaped spring 91 outwardly towards the sleeve 6. At the same time, the lever 7 is biased by the retracting spring 92 towards the clutch hub 3 at places where the lever 7 has a constant thickness. Hence, the lever 7 always closely contacts the clutch hub 3.
When the sleeve 6 is slidably moved towards the gear piece 41 in the axial direction of the shaft 2 from the neutral state, as illustrated in FIG. 6B, the inclined surface 64 press-contacts the key portion 711 of the lever 7. As a result, the lever 7 is pressed towards the gear piece 41 in a sliding direction of the sleeve 6 so as to resist the biasing force applied by the retracting spring 92. The lever 7 transmits pressing force received at the inclined surface 64 to the synchronizer ring 5. The pressing force is generated by the sleeve 6 being moved towards the gear piece 41 so as to engage the inclined surface 64 of the spline 61 formed on the sleeve 6 with the key portion 711 of the lever 7. Specifically, the key portion 711 of the lever 7 functions as a point where the pressing force is applied (power point), the end portions 72 function as fulcrum, and the top portion 71 of the half-ring shaped portion functions as a point of application of the pressing force (working point) to which the pressing force of the sleeve 6 is transmitted via the lever 7. The lever 7 transmits the pressing force of the sleeve 6 using the power point, the fulcrum and the working point to a contacting surface 52 of the synchronizer ring 5. The contacting surface 52 contacts the top portion 71 of the half ring-shaped portion of the lever 7 facing the ring gear 41.
The synchronizer ring 5 is moved towards the gear piece 41 by receiving the pressing force at the contacting surface 52. When the sleeve 6 is further moved towards the gear piece 41, as illustrated in FIG. 6C, the key portion 711 of the lever 7 is disengaged from the inclined surface 64 against the biasing force of the C-shaped spring 92 being applied outwardly towards the sleeve 6 (in the radial direction of the sleeve 6), and then the key portion 711 of the lever 7 is inserted along an inner circumference of the spline 61 of the sleeve 6.
When the lever 7 is inserted along the inner circumference of the spline 61 of the sleeve 6, radius of the C-shaped spring 91 is narrowed so as to narrow or close the opening of the C-shaped spring 91. Therefore, the key portion 711 of the half ring-shaped portion is disengaged from the inclined surface 64 of the spline 64 formed on the sleeve 6. As a result, the pressing force of the sleeve 6 is not applied to the half ring-shaped portion of the lever 7.
In the above-mentioned manner, the synchronizing operation between the clutch hub 3 and the gear piece 4 is implemented by gradually increasing frictional force generated by the inner conical surface 51 of the synchronizer ring 5 being pressed with the outer conical surface 411 of the gear piece 41. After the synchronizing operation is completed, the sleeve 6 is further slid towards the gear piece 41, and then a shifting operation is completed.
The synchronizing operation for synchronizing the clutch hub 3 and the gear 4 is completed with the synchronizer ring 5, the lever 7, the C-shaped spring 91 and the retracting spring 92.
The known lever-type synchronizer device includes the synchronizer ring 5, the lever 7, the C-shaped spring 91 and the retracting spring 92 as main components for the synchronizing operation in order to fulfill the synchronizing function. In other words, the number of components used for the known lever-type synchronizer device tends to increase, which may increase manufacturing costs of the lever-type synchronizer device.
A need exists for a synchromesh which is not susceptible to the drawback mentioned above.